Fighting Defensively as a Standard Action
You can choose to fight defensively when attacking. If you do so, you take a -4 penalty on all attacks in a round to gain a +2 dodge bonus to AC for the same round. See also: Fighting Defensively as a Full-Round Action.

Fighting Defensively as a Full-Round Action
You can choose to fight defensively when taking a full attack action. If you do so, you take a -4 penalty on all attacks in a round to gain a +2 dodge bonus to AC for the same round.

Total Defense
You can defend yourself as a standard action. You get a +4 dodge bonus to your AC for 1 round. Your AC improves at the start of this action. You can’t combine total defense with fighting defensively or with the benefit of the Combat Expertise feat (since both of those require you to declare an attack or full attack). You can’t make attacks of opportunity while using total defense.